Motor honda prelude 1989 2.0 si?

i have a honda prelude 1989 2.0si i only had it for a little while and when i was driving the RPM's when down and the check service soon light came on and now my car wont start i already put in a new main relay switch a mechanic told me it was the timing chain and that it would be best if i get a motor cause if the timing chain broke then the head is no good were can i buy a motor please help as soon as possible